The present invention relates to a brake system, more particularly for automotive vehicles, comprising a master cylinder, wheel cylinders as well as a device for anti-lock control.
Brake systems have become known, see e.g. German printed and published patent application No. P 36 41 712.2, which are equipped with an anti-lock control system as well as with auxiliary pumps. These auxiliary pumps deliver pressure fluid into the working chambers of the master cylinder and into the wheel cylinders during the anti-lock control mode. According to a control algorithm, the wheel cylinder volumes are discharged into an unpressurized supply reservoir in the phase of pressure reduction. For the purpose of pressure modulation in the wheel cylinders, inlet and outlet valves are used which are allocated to the wheel cylinders. These inlet valves and outlet valves form the so-termed pressure modulator of the anti-lock control system. In the control mode, it is possible that so much pressure fluid will be discharged through the pressure modulator, (i.e., through the outlet valves for the pressure-modulated wheel cylinders) that the pressure fluid pump will not be able to compensate for this pressure fluid discharge by an increased volume of delivery.
In known systems; the pump, the pressure modulator and the pressure chamber of the master cylinder are hydraulically interconnected in such a manner that pressure fluid out of the pressure chamber of the master cylinder is allowed to discharge through the pressure modulator into the unpressurized supply chamber. If the delivery rate of the pump is not sufficient to compensate for the pressure fluid discharged, too much pressure fluid will be discharged from the pressure chamber of the master cylinder. Under the action of the brake pedal force or the force of the brake power booster, there will then occur undesirable movement of the piston of the master cylinder in the direction of the bottom of the master cylinder. In an extreme case, the piston will move into its most activated end position and, since the piston and the brake pedal are interconnected in terms of effect, the brake pedal may be depressed through its full travel. In such case, anti-lock control would be disconnected for safety reasons since an insufficient amount of volume is available for performing the anti-lock control function.
In the event of the brake pedal being shifted from the nominal position provided for the control mode, the actuation comfort will be diminished.